The Prisoner
by rbvictor
Summary: When Finn and Jake accidentally release an ancient evil from the palace dungeon, its up to them to track him down. But who is this prisoner, and more importantly what is Princess Bubblegum hiding? rated T to be safe.
1. Chapter 1

**Warning I don't own Adventure Time or any of its characters. I only own my OC Roy. **

_The Candy Kingdom outside Princess Bubblegum's castle_

"Thanks for helping me pack for the science convention Finn." Princess Bubblegum said as she hopped on her giant flying swan.

"No problem PB." Finn said as he passed her a suitcase.

"Now remember Finn, what ever you do don't go down in the old castle dungeon." Princess Bubblegum explained as she prepared to take off. "The dungeon contains one of the most dangerous criminals to ever plague the Candy Kingdom."

"Who is it?" Jake asked intrigued.

"Yah PB who is this guy? Finn asked.

"We do not speak his name. He has been in that dungeon ever since my parents ruled the Candy Kingdom." Princess Bubblegum said with a dark expression on her face. "Just promise me you won't go into the dungeon."

"Alright Princess." Finn said disappointed. Princess Bubblegum then flew away on her swan.

"So what do you want to do now Jake?" Finn asked as they walked back into the castle.

"Hey lets check out that dungeon." Jake replied.

"We just promised Princess Bubblegum that we wouldn't go down there." Finn said responsibly.

"I know." Jake said sadly. "Hey Finn, Bubblegum said that the prisoner had been down there for years right?"

"Yah, why?" Finn said confused.

"Well how do know he hasn't escaped." Jake said

"We don't." Finn said starting to understand where the conversation was going.

"The responsible thing to do would be to check the dungeon and see if he's still there, right?" Jake said.

"Your right." Finn said as he stopped in front of the dungeon door. Finn then opened the door and peered into the dark. The dungeon consisted of a long set off stairs with a stone door at the end.

"What's that?" Jake asked lifting his ears.

"What's what?" Finn said.

"You don't hear that?" Jake asked.

"I don't hear anything." Finn replied. "Come on." Finn then drew his sword started walking down the stairs. As he reached the bottom he paused. Finn could just make out the sound of an electric guitar coming from the other side of the door.

"What the math?" Finn said as he pushed the cell door open.

**Well what do you think so far? Feel free to message or review if you have any questions or suggestions. **

**P.S. For another great adventure time fanfic check out Teller14-djb's Into the Wormhole.**


	2. Who are You?

**Warning! I do not own Adventure Time or any of its characters. Before we begin I would like to thank Teller14-djb for his review, for those of you who haven't yet checked out his story Into the Wormhole, you won't regret it. Now without further delay, on with the show!**

"Hello?" Finn said as he stepped into the cell. The stone walls were covered with a thick layer of frost that someone had scratched various notes and drawings in. A boy who looked to be only a few years older Finn was laying on the bed absent- mindedly strumming a guitar that seemed to be made completely of frost. His skin was as white as snow and his pale blue eyes gleamed with defiance and madness. His hair was a dull grey that seemed out off place with his white cloak.

"Who are you?" The boy said staring at Finn with a look of confusion.

"My name is Finn," Finn said pointing his sword at the boy. "Now who are you, and what did you do to get locked up?"

"Who am I?!" The prisoner said looking down at his guitar. He stared at his reflection for a few moments before asking softly. "Who am I?"

"Hey Finn, did you find out who the prisoner is yet?" Jake said as he walked into the cell leaving the door open a crack.

"No, I don't even think he knows." Finn said astonished.

"It looks like he has poo brain man." Jake said looking at the boy still staring at his reflection. "Come on; let's go beat up Ice King or something."

Suddenly the prisoner threw his guitar at Jake's head. Jake ducked out-of-the-way in time and the guitar shattered against the wall.

"What was that for?" Jake said as the prisoner shot to his feet. His eyes were now a blood-red color.

"I shall encase this world in an endless winter, and nothing shall stand in my way! Kneel before the Prince of Frost!" the Frost Prince said in a voice laced with insanity.

"You'll have to get past me first!" Finn said as he charged at the Frost Prince with his grass sword. The Frost Prince used his powers to form two short swords made completely of frost. Finn swung his sword at the Frost Prince's head but he blocked the blow by catching Finn's sword with his blades.

"What the Glob!" Finn exclaimed as frost began forming on his grass sword.

"My powers far exceed your swordsmanship, surrender now and perhaps I'll spare your lives!" Frost Prince said as he backed Finn against the wall.

"A little help here Jake!" Finn said as he pulled his sword free.

Jake swung a giant fist at the Frost Prince but he jumped to the side at the last-minute. Frost Prince's eyes then began to glow white as he shot bolts of frost out of is swords and encased Jake in a ice.

"Jake!" Finn shouted looking at his best friend. The Frost Prince took advantage of this distraction and knocked Finn to the ground.

"Prepare to meet your fate, hero!" Frost Prince said as his eyes started glowing again. Suddenly the cell door burst open.

"Stop, Roy!" Princess Bubblegum shouted from the doorway.

"Bonnie?" Frost Prince/ Roy said as his eyes began to shift back to blue. However the change lasted only a few seconds before they shifted back to red. With a roar Frost Prince ran for the door and threw Princess Bubblegum aside. By the time PB got back on her feet Frost Prince had already escaped. Princess Bubblegum then turned back to Finn who was in the process of freeing Jake.

"I told you not to enter the dungeon, Finn!" Princess Bubblegum said.

"How did you know we were down here?" Finn asked curious about PB's sudden appearance.

"I had a motion sensor installed to alert me if the prisoner ever tried to escape." Princess Bubblegum answered showing Finn a hand-held device.

"So who was that guy and why did you call him Roy?" Finn asked

"His name is Roy Albert Bubblegum." Princess Bubblegum said unable to look Finn in the eye. "He's my brother."

**Who is Roy Albert Bubblegum? Why does he now call himself Frost Prince? Why are his powers similar to Ice King's? When will I stop asking questions? Tune in next week for the answers. In unrelated news any and all reviews are appreciated. If anyone has any questions or suggestions please feel free to message me.**


	3. A trip down memory lane

**Warning! I don't own Adventure time or any of its characters. I only own my OC Roy. I would like to thank Teller14-djb and an anonymous guest for reviewing. Now on with the show!**

"The Frost Prince is your brother!" Finn said having trouble processing the information.

"He wasn't always the Frost Prince, Finn." Princess Bubblegum replied. "It all started when I was a little girl…"

_A very long time ago…_

A slightly younger Frost Prince stands holding a picture in a lab in the unfinished castle. His skin is blue instead of white and his hair is a dark black. Instead of a white cloak, he wears a lab coat. Suddenly a ten-year old Princess Bubblegum enters the lab.

"Roy, Marceline is here to see you." The young princess said.

"Thanks Bonnie." Roy replied setting the photograph down. Roy and Bonnie walked to the entrance of the castle to meet Marceline.

"Hey Marceline, have you considered my offer?" Roy asked.

"I don't know Roy." Marceline said nervously. "What if something goes wrong?"

"You worry too much." Roy said shaking his head slightly.

"What are you two talking about? Princess Bubblegum asked.

"You remember Marceline's friend the Simon?" Roy asked turning towards his sister.

"He was kind of creepy." Princess Bubblegum replied.

"Yes, I suppose he was." Roy said with a smile. "Now, what if I were to tell you that Simon wasn't always that way. You see, Simon is suffering from a curse, a curse that I believe I may have found a cure for."

"Really!" Princess Bubblegum said amazed.

"I don't know Roy, it still doesn't seem safe." Marceline said unsure.

"Don't worry Marcy, I'll be fine." Roy replied confidently.

"_Roy then spent the next month running various tests on samples of the Ice King's blood trying to create a cure to his curse. He became obsessed with his research of human sciences while looking for the cure, eventually it lead him to rediscover several lost technologies such as nuclear energy." Present day Princess Bubblegum explained. "Then one day he asked Marceline and me to come to the lab…."_

"I've finally done it!" Roy said as Marceline and his sister entered the lab. "I've found the cure!"

"That's great!" Marceline exclaimed. "I'll go get Simon."

"Hold on Marceline, there is still one more test to run." Roy said holding up a syringe.

"Are you insane?" Marceline exclaimed as Roy injected himself.

"Don't worry Marcy." Roy replied with visible effort as the serum began to take effect. "The syringe contained a modified version of Simon's curse. If my calculations are correct it should only give me Simon's powers of ice but without causing me to go crazy. Once I know the serum works I can then inject Simon."

Suddenly Roy doubled over in pain. His hair began to change from black to grey and his skin lost all color. His lab coat morphed into a pure white cloak.

"Roy!" Marceline shouted as she rushed to help him stand.

"I …must have …. miscalculated!" Roy gasped as he turned his head towards Marceline. His eyes were begging to turn red. "The amulet on the table…. give it to Bonnie….Run Marcy run!" Roy then collapsed on the ground.

"Roy?" Princess Bubblegum asked.

"There is no Roy." Roy said as he stood up with a voice laced with evil and insanity. "There is only the Frost Prince!"

Frost Prince then used his new powers to shoot beams of ice at Princess Bubblegum but the young Princess ducked out of the way in time. Marceline quickly grabbed a picture and the amulet off the table and dragged Princess Bubblegum from out of the lab.

"There's no where you can run!" Frost Prince shouted as Marceline and PB fled the castle.

"_For the next three weeks the Frost Prince terrorized the Candy Kingdom. My parents raised an army to capture my brother but he was more powerful than even they could have imagined."_

Frost Prince stands in the middle of a battle field on a rainy night. The entire Candy Kingdom army lies in ruins before him. He walks across the field until he reaches two figures frozen in a solid block of ice. He picks up a sword from a fallen solder.

"No one shall stand in my way!" The Frost Prince shouts as he shatters the ice and the bodies inside. Two crowns fall to the ground among the debris.

"Roy you've got to fight it." Marceline shouts as she flies over the carnage.

"No one tells the Frost Prince what to do!" Frost Prince exclaims as he charges Marceline, who blocks the blow with her ax. Suddenly Roy's eyes begin to shift back to blue.

"Marceline, you have to kill me." Roy pleads.

"I…I can't Roy!" Marceline replies with tears in her eyes.

"Marceline, please! I can feel my mind slipping away a little more every day. The curse awakes the darkest parts of you and my formula just made it worse. The Frost Prince intends to destroy the world as we know it and thanks to my research he has the power to do it! You must kill me before…before..." Roy's eyes once again turn red. The Frost Prince swung his sword at Marceline's head but she ducked to the side. She countered by bashing Frost Prince on the head with the handle of her ax. The Frost Prince fell back in the mud unconscious. Marceline raises her ax for the final blow but instead embeds the ax into the ground mere inches from the Frost Princess's head.

"I'm sorry." Marceline says as she sinks to her knees crying. After five minutes Marceline slowly stands up and picks up both Roy and the two crowns. She flies to the castle where Princess Bubblegum is waiting for news of the battle.

"I take it the mission was successful?" The young princess asked seeing Roy's unconscious form, only then does she notice the two crowns in Marceline's hand. "No! They can't be…" Princess Bubblegum said on the verge of tears.

"I'm sorry; I was too late to save them." Marceline said sadly. "We need to deal with Roy before he wakes up though, or their sacrifice will mean nothing."

"There is a dungeon deep within the castle." Princess Bubblegum replied. "He won't be able to escape that."

They proceed to lock Roy in the dungeon, but before they exit Marceline stops suddenly. She reached into her pocket and pulled out the photo she took from the lab. It is a picture of Roy and Marceline smiling, holding hands on a hill watching a meteor shower.

"Good bye Roy." Marceline said as she dropped the photo over the stairwell and exited the dungeon.

**I love a good flashback. As usual feel free to review or ask questions. Tune in next week for chapter 4.**


	4. The Lab

**Warning! I do not own Adventure Time or any of its characters. I only own my OC Roy. **

"I've spent years trying to find a cure to my brother's curse." Princess Bubblegum said as she finished her story. "Unfortunately all he kept his research hidden in his personal lab. Even I don't know where it is."

"Maybe he left a clue." Finn said hopefully.

"Well, there is this amulet." PB said as she pulled out the amulet. It was a sphere of black stone rimmed in silver with a gold chain.

"Let me see that." Jake said as he grabbed the amulet. Suddenly, silver writing began to form on the amulet. "What the glob!" Princess Bubblegum quickly took the amulet back.

"_Scientia Sit Potentia._ This is Latin!" PB exclaimed.

"What's Latin?" Finn asked.

"Latin is an old language, Finn. My brother taught me how to read some of it. I think it means _knowledge is power._" Princess Bubblegum explained. As soon as she translated the phrase the amulet began to glow, a hologram of Roy from before the transformation appeared.

"_Bonnie, if you're listening to this then my experiment failed. If this is true then there is only one way to save me. Hidden near Marceline's house is my secret lab, this amulet will guide you there. Inside is all my research on curing the curse, as well as the means to destroy me if all else fails. The safety of the Candy Kingdom must come before all else, and if I become too big a threat then you must kill me."_ The hologram of Roy said sadly. _"I'm sorry it had to come to this. Good luck."_ The hologram then disappeared.

"We have to get to Marceline's cave before the Frost Prince can do too much damage!" PB exclaimed.

"Hold on!" Jake said as he picked up Finn and PB and set them on his back as he grew into a giant. Jake then started walking towards Marceline's, covering miles with each step.

_One ride across Ooo later_

"We're here." Finn said as he hoped off Jake's back onto the cave floor.

"But where's the lab?" Jake asked as he shrunk back to his normal size.

"What's the amulet say PB?" Finn asked as Princess Bubblegum pulled out the amulet. Suddenly a compass arrow appeared on the stone pointing at the cave wall.

"Over here." PB said as she walked over to the wall. When she got close, the wall a section slide away to reveal the lab.

"This place is amazing!" Finn exclaimed as he walked into the lab. The lab contained several half finished inventions all surrounding what appeared to be a nuclear reactor.

"I found the research." Princess Bubblegum said holding up a stack of papers. Suddenly Marceline walked into the lab.

"What's going on guys?" Marceline asked wondering why they were in her cave.

"We accidentally released the Frost Prince and now we got to find a cure for the curse before he destroys all of Ooo!" Finn explained.

"What?! Do you realize what you've done! I was barely able to stop Roy the first time!" Marceline shouted.

"Don't worry Marceline, we've got the formula for the cure. Right PB?" Jake said unconcerned.

"I just have to find out what went wrong the first time and then I can make the cure." Princess Bubblegum said without looking up from the paperwork.

"You don't understand we don't have time to wait for the cure." Marceline exclaimed. "When I stopped Roy the first time he was working on something big. Something that could have changed the face of Ooo forever."

"What was it Marceline?" Finn asked.

"A nuclear bomb!" Marceline said ominously.

**Sorry for the delay. Hopefully I will update again next week. **


	5. Writing on the Wall

**Warning! I do not own Adventure Time or any of its characters. I only own my OC Frost Prince/ Roy. Now on with the show!**

"A nuclear bomb!" PB shouted alarmed.

"What's a nuclear bomb?" Finn asked confused.

"A nuke was the most powerful weapon of the Mushroom wars Finn." Marceline explained. "It created a massive explosion while releasing devastating amounts of radiation into the surrounding area. But the effect the Frost Prince is counting on is the so-called nuclear winter; a winter that would last for decades."

"We have to stop him before he can finish building the bomb!" Princess Bubblegum exclaimed. "The fate of the Candy Kingdom depends on stopping Roy once and for all."

"Alright Princess, Jake and I will find and defeat the Frost Prince while you work on the cure." Finn said confidently.

"How will you even find him? He could be any where." Marceline pointed out.

"I know where to start." Finn replied.

_One trip back to the dungeon later_

"Everyone take a wall, we're looking for any clues to where the bomb might be." Finn said as Jake and Marceline followed him into the cell.

"All I've got is musical notes. Hey, that's catchy!" Jake exclaimed after a few minutes as he looked at his wall_._

"Hey guys over here!" Marceline shouted from beside the bed. "It looks like some kind of journal entry. _I've finally regained my sanity today, but I don't know how long it will last. I leave behind this record so that my story will not be forgotten. With each passing day the Frost Prince's will grows stronger. Now I know how Simon feels trapped inside his head helplessly watching as the curse controls his body. I should have never taken the serum in the first place but my pride got the best of me. My only regret that I shall never again see my beloved Marceline. If you ever read this Marcy, know that I forgive you for not killing me when you had the chance. I can only hope you can forgive me for the things I've done. I know that the Frost Prince murdered my parents and that Bonnie will probably never forgive me. She will be a better ruler than I would have been. If you're wondering about where the Frost Prince hid his master plan, check the mountains near Simon's Ice palace. If you discover the hideout keep an eye out for my old guitar in the throne room. It may not make up for the pain I've caused you, but I hope it will remind you of better days. _

_Signed _

_Prince Roy Albert Bubblegum_

"Wow." Finn said unsure what else to say.

"This was the only thing I could find that wasn't raving about covering the world in ice." Marceline said with tears in her eyes.

"Well what are we waiting for?" Jake said heading towards the door. "We have a secret hide out to find!"

**Poor Roy. Anyway, sorry about the short chapter but I needed to set stage for the next one. If anyone has any questions, suggestions, or requests please feel free to message me. Tune in next week for chapter 6 and more combat scenes. **


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